by NCERT Solved Exercise Questions – Class 11 Biology Chapter 20 Locomotion and Movement
20.1 Draw the diagram of a sarcomere of skeletal muscle showing different regions.
Ans – diagrammatic representation of a sarcomere
20.2. Define sliding filament theory of muscle contraction.
Ans – The process of muscle contraction, in which the thick filaments slide over the thin filaments to shorten the myofibril, is explained by the sliding filament theory.
Actin and myosin, two distinct contractile proteins, alternately adorn the light and dark bands of each muscle fibre. The I-band, or actin, is a thin contractile protein found in the light band; the A-band, or myosin, is a thick contractile protein found in the dark band. Each I-band is split in half by an elastic fibre known as the z line. The z line is firmly attached to the thin filament. The H-zone is the central region of the thick filament that is not covered by the thin filament.
The thin filaments are in intimate contact with the myosin heads or cross bridges during muscle contraction. The thin filaments are consequently drawn toward the centre of the sarcomere. The actin filaments’ Z line is likewise pulled, shrinking the sarcomere as a result. As a result, the I-band shrinks and the H-zone vanishes but the band’s length stays fixed at its initial value.
20.3. Describe the important steps in muscle contraction.
Ans – A motor neuron sends a signal to the central nervous system (CNS) that causes the muscle to contract. A motor unit is made up of a motor neuron and the muscle fibres that connect to it. The neuromuscular junction, also known as the motor-end plate, is where a motor neuron meets the sarcolemma of a muscle fibre. When a brain signal reaches this junction, it causes the neurotransmitter acetylcholine to be released, which causes the sarcolemma to produce an action potential. This causes calcium ions to leak into the sarcoplasm and disseminate throughout the muscle fibre. An rise in Ca++ levels causes calcium to bind to a troponin subunit on actin filaments, removing the masking of myosin active sites in the process.
The myosin head now attaches to the exposed active sites on actin to create a cross bridge using the energy from ATP hydrolysis. As a result, the connected actin filaments are drawn toward the A-bonds’ centre. These processes also result in a pulling inward of the Z-line, which shortens the sarcomere and causes contraction. The a-bonds remain the same length while the ‘I’ bonds shrink during the contraction of the muscle, as is evident from the aforementioned processes. Myosin returns to its relaxed state after releasing ADP and p1.
When a fresh ATP bonds, the cross-bridge is destroyed. This results in Z-lines relaxing and returning to their initial position.Distinct muscles have different fibres with different response times. When muscles are activated repeatedly, the anaerobic breakdown of their stored glycogen can result in an accumulation of lactic acid and tiredness. Myoglobin, an oxygen-storing pigment with a red hue, is found in muscle. Some of the muscles have high myoglobin concentrations, giving them a crimson hue. These muscles go by the name “Red Muscles.” These muscles also have a lot of mitochondria, which may use a lot of oxygen that is stored in them to produce ATP.
Therefore, these muscles can also be referred to as aerobic muscles. On the other hand, some of the muscles have very little myoglobin and look yellowish or pale as a result. The white fibres are those. The number of mitochondria is also few in them, but the amount of sarcoplasmic reticulum is high. They depend on the anaerobic process for energy.
20.4. Write true or false. If false change the statement so that it is true.
(a) Actin is present in thin filament
(b) H-zone of striated muscle fibre represents both thick and thin filaments.
(c) Human skeleton has 206 bones.
(d) There are 11 pairs of ribs in man.
(e) Sternum is present on the ventral side of the body.
Ans –
- (a)True
- (b)False: The H-zone of striated muscle fibre represents only thick filaments.
- (c)True
- (d)False: There are 12 pairs of ribs in man.
- (e)True
20.5. Write the difference between :
(a) Actin and Myosin
(b) Red and White muscles
(c) Pectoral and Pelvic girdle
Ans –
(a) Actin and Myosin
(b) Red and White muscles
| Red muscle fibre | White muscle fibre | ||
| 1 | Red muscle fibres are thin and smaller in size. | 1 | White muscle fibres are thick and larger in size. |
| 2 | They are red in colour as they contain large amounts of myoglobin. | 2 | They are white in colour as they contain small amounts of myoglobin |
| 3 | They contain numerous mitochondria. | 3 | They contain less number of mitochondria. |
| 4 | They carry out slow and sustained contractions for a long period. | 4 | They carry out fast work for short duration. |
| 5 | They provide energy by aerobic respiration. | 5 | They provide energy by anaerobic respiration. |
(c) Pectoral and Pelvic girdle
20.6. Match Column I with Column II :
Column I Column II
(a) Smooth muscle (i) Myoglobin
(b) Tropomyosin (ii) Thin filament
(c) Red muscle (iii) Sutures
(d) Skull (iv) Involuntary
Ans – (a)– (iv)
(b)-(ii)
(c) -(i)
(d) – (iii)
20.7. What are the different types of movements exhibited by the cells of human body?
Ans – Human body cells move in three different ways: amoeboid, ciliary, and muscular motions. Some specialised cells in our bodies, such as blood leucocytes and macrophages, move in an amoeboid manner. It is impacted by pseudopodia created by protoplasmic streaming (as in Amoeba). The amoeboid movement also involves cytoskeletal components like microfilaments.
Amoeboid movement is a characteristic of leucocytes found in blood. These blood cells migrate from the circulatory system to the site of the injury when tissue is damaged in order to start an immune reaction.
Ciliary mobility is a characteristic of reproductive cells like sperm and eggs. This movement aids in the ova’s transit via the fallopian tube and into the uterus.
Muscle movement is visible in muscle cells.
20.8. How do you distinguish between a skeletal muscle and a cardiac muscle?
Ans –
20.9. Name the type of joint between the following:-
(a) atlas/axis
(b) carpal/metacarpal of thumb
(c) between phalanges
(d) femur/acetabulum
(e) between cranial bones
(f) between pubic bones in the pelvic girdle
Ans – (a) atlas /axis: Pivotal joint
(b) carpal /metacarpal of thumb: Saddle joint
(c) between phalanges: Hinge joint
(d) femur /acetabulum: Ball and socket joint
(e) between cranial bones: Fibrous joint
(f) between pubic bones in the pelvic girdle: Cartilaginous joint
20.10. Fill in the blank spaces:
(a) All mammals (except a few) have __________ cervical vertebra.
(b) The number of phalanges in each limb of human is __________
(c) Thin filament of myofibril contains 2 ‘F’ actins and two other proteins namely __________ and __________.
(d) In a muscle fibre Ca++ is stored in __________
(e) __________ and __________ pairs of ribs are called floating ribs.
(f) The human cranium is made of __________ bones.
Ans – (a) Seven
(b) Fourteen
(c) Troponin, tropomyosin
(d) Sarcoplasmic reticulum
(e) 11th, 12th
(f) Eight
